Publish this image again as moodlehq/moodle-db-oracle-r2

[stronk7]

As far as the source image for this was re-allowed by Oracle some months ago and we are already using it, see #6 , and part of some changes happening @ DockerHub, planned @ ICT-759, this in an issue about to:

• start publishing a new moodlehq/moodle-db-oracle-r2 (the old name is still "locked" and cannot be used) public image.
• start using it instead of current private image.
• amend docs here and there to point to the new image.
• cross fingers and wish Oracle won't ask again for any removal as far as they authorized the one we are extending with just a few customizations.

Ciao :-)